Iodine is a trace element required by the thyroid gland to produce thyroxine and triiodothyronine, thyroid hormones necessary for multiple processes related to normal growth and development. Iodine deficiency has many adverse effects, collectively termed iodine deficiency disorders, including hypothyroidism, goiter, cretinism, stillbirths, and delayed psychomotor and cognitive development (Carson BL, et al, 1986; Hallowell JG, et al, 1998). The most critical period for iodine sufficiency is in utero through the first two years of life when thyroid hormones are required for normal brain development (Sieler H.G., et al, 1988). Maternal iodine deficiency and hypothyroidism have been associated with impaired cognitive and psychomotor development in the offspring (World Health Organization, 1991; Thomas R, 2004).
NHANES measured urinary iodine concentration (UIC) in a 1/3 subsample of examined participants aged 6 years and over, including pregnant women. Additionally, UIC was measured in stored urines for examined pregnant participants in the remaining 2/3 sample. Urinary iodine data was then pooled from all pregnant women in survey cycle 2009-2012 in this special dataset to facilitate analysis related to maternal iodine status.
Due to the disclosure concern, this dataset is only available through the NCHS Research Data Center (RDC).
All pregnant women aged 8-59 years examined in 2009-2012 were eligible.
Urine specimens were processed, stored, and shipped to the Division of Laboratory Sciences, National Center for Environmental Health.
Detailed instructions on specimen collection and processing can be found in the NHANES Laboratory Technologists Procedures Manual (LPM).
UIC was analyzed by inductively coupled plasma mass spectrometry, which is the gold standard method (Tanner SD, et al, 1999; Tanner SD, et al, 2002). See documentation for NHANES 2011-2012 Urinary Iodine file (UIC_G) for more information. Iodine was quantified based on the peak as a ratio of analyte to internal standard tellurium. The limit of detection, equal to 3*S/N, where S/N is the signal to noise derived from the measurement process as the concentration approaches zero, was calculated. Two concentration levels of quality controls were analyzed in each analytical batch. Reported results for accuracy and precision were compared to specifications of the quality control/quality assurance program of the Division of Laboratory Sciences, NCEH, CDC (Caudill SP, et al, 2008). Absolute assay accuracy were verified from analysis of the National Institute of Standard Technology 2670A, 2672a and 3668 Standard Reference Materials. Electrical signals resulting from the detection of the ions were processed into digital information that is used to indicate the intensity of the ions and subsequently the concentration of the element.
Refer to NHANES 2011-2012 Lab Methods for Iodine & Mercury for detailed description of the laboratory method used.
The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES LPM.
The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.
Refer to the 2009-2010 and 2011-2012 Laboratory Data Overview for general information on NHANES laboratory data.
In 2009-2012, UIC was measured in a 1/3 subsample of examined participants aged 6 years and over, including pregnant women. Additionally, UIC was measured in stored urines from examined pregnant participants in the remaining 2/3 sample. This special dataset only includes UIC data for all pregnant women in NHANES 2009-2012 and is only available through the NCHS Research Data Center (RDC). The UIC data from the one-third sample of examined participants aged 6 years and older is available publically at the NHANES website (i.e., UIC_F and UIC_G).
The analysis of NHANES 2009-2010 and 2011-2012 laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2009-2010 and 2011-2012 Demographics Files contain demographic data, health indicators, and other related information collected during household interviews as well as the sample weight variables. The demographics file may be linked to the laboratory data file using the unique survey participant identifier (i.e., SEQN).
The MEC exam sample weights should be used to analyze these data. Data users need to be aware that pregnant women are not part of the sampling scheme for NHANES 2009-2012 and given the small sample size of this dataset any inference to being nationally representative should be interpreted with caution. Please refer to the NHANES Analytic Guidelines and the online NHANES Tutorial for further details on the use of sample weights and other analytic issues.
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